Exposed die pad package with power ring

ABSTRACT

A packaged semiconductor is disclosed. The packaged semiconductor comprises a conductive integral frame that includes an inner portion and a ring portion encircling the inner portion, a semiconductor die that is mounted to a first surface of the inner portion of the conductive frame, and a casing that supports the conductive frame and covers the semiconductor die. Sections of the conductive frame that connect the inner portion to the ring portion are removed after the casing is applied to the conductive frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/167,726, filed on Apr. 8, 2009. The disclosure of the aboveapplication is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to semiconductor packaging and moreparticularly to exposed die pad packages including a power ring.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Semiconductor devices are generally manufactured on a silicon wafer.Each silicon wafer undergoes various processing steps to create multipleindividual devices on the wafer. Each device on the wafer is referred toas a die. When the wafer is complete, the wafer is divided into theindividual dies (or, dice). For example only, this dividing may beperformed by sawing or by scoring and snapping.

The dice are generally vulnerable to their environment. For exampleonly, the dice are physically fragile and prone to cracking and breakingwhen being handled. In addition, the dice are prone to contamination,both by physical contact as well as by airborne particles. The dice arealso very sensitive to electrostatic discharge. For these and otherreasons, the dice are often packaged. The packaged dice, or chips, aremuch easier to handle and may be easier to use in applications such asprinted circuit boards.

A package may include one die or may include multiple dice. For ease ofexplanation, the following description will refer to a single die,although the present application applies to the packaging of multipledice into a single package.

An exemplary package includes a first package piece to which the die ismounted. The first package piece includes a first face and a secondface. The first face includes a die attach area where the die is placed.The second face may include features for electrically and mechanicallyconnecting the package to a printed circuit board. Leads carryelectrical signals from the die to the printed circuit board. Portionsof the leads may be located on the first face of the first packagepiece.

When the die is secured to the die attach area of the first packagepiece, wire bonds may be formed between bond pads of the die and theleads. The leads may be bent so that they wrap around the edges of thefirst face and protrude past the second face. The leads can therefore beinserted into through-holes of a circuit board. Often, leads areattached to two opposing edges of the first face. This creates two rowsof protruding leads, and the package is called a dual inline pin (DIP)package.

Through-holes may make circuit board layout more difficult and mayprevent components from being placed on both sides of the circuit board.Surface mounting technology, where leads do not protrude through thecircuit board, avoids these problems. The leads of a surface-mountpackage are generally bent to be parallel to the second face, andtherefore present flat contacting surfaces to corresponding receivingpads on the circuit board.

Traditionally, leads have been located around the perimeter of thepackage. This is because the die occupies the center of the package andthe bond wires connect outward from the die to the perimeter of thepackage. A surface-mounted version of the DIP package is a small-outlineintegrated circuit (SOIC), where the leads are bent outward when theyreach the second face to form a gull-wing shape.

When the package has leads on all four edges, the package may bereferred to as a quad flat package (QFP). When the leads do not extendbeyond the edges of the package, the package may be referred to as aquad flat no-leads package (QFN). Some QFN packages include a centralpad on the second face that dissipates thermal energy from the packageto the circuit board.

To allow for greater connection density, leads may be formed in theinterior area of the second face of the package. Internal wiring of thepackage may route signals from where bond wires connect at the perimeterof the package on the first surface to interior leads on the secondsurface of the package.

As described above, the face of the die has traditionally been exposedand bond wires connect the exposed bond pads of the die to leads of thepackage. In flip-chip packaging, the die is inverted onto the package,causing the bond pads of the die to contact the first face of thepackage. Then, the die can be designed to include bond pads in thecenter of the die, which will be located above the center of thepackage. This decreases the need for special conductors within thepackage that route signals from the perimeter of the first face to thecenter of the second face.

In one example, package leads are in the form of pins; such a package iscalled a pin grid array (PGA). Pin grid array packages may mount to asocket that is surface-mounted to the circuit board. In another example,the package includes an array of pads that connects to an array of padson the circuit board. A ball of solder may be placed on each of thepackage pads; such a package is called a ball grid array (BGA).

A land grid array package includes pads that interface with pads on thecircuit board. However, the land grid array package does not includeballs of solder on the package pads. Instead, the circuit board may havea layer of solder on the pads. The solder may be restricted to the padlocations by using a mask when applying the solder. Once the package ispositioned on the circuit board, the solder can be reflowed to secureeach of the package pads to each of the receiving pads of the circuitboard.

Alternatively, a socket may be connected to the circuit board. Thesocket applies clamping force to the package. This clamping force caneither force the package pads to contact pads of the circuit board orcause the package pads to contact pads of the socket. A socket may allowfor easy replacement of the package.

Once the die is mechanically and electrically connected to the firstpiece of the package, the die is covered. This isolates the die and anyother components, such as bond wires, from the environment. The die maybe covered by attaching a second package piece, such as a lid, to thefirst piece of the package. The first and second pieces may be sealed toprevent any contaminants from entering the space where the die islocated.

SUMMARY

A packaged semiconductor is disclosed. The packaged semiconductorcomprises a conductive integral frame that includes an inner portion anda ring portion encircling the inner portion, a semiconductor die that ismounted to a first surface of the inner portion of the conductive frame,and a casing that supports the conductive frame and covers thesemiconductor die. Sections of the conductive frame that connect theinner portion to the ring portion are removed after the casing isapplied to the conductive frame.

The ring portion includes a continuous first ring portion that encirclesat least three sides of the inner portion. In one embodiment, thecontinuous first ring portion completely encircles the inner portion.

In one embodiment, the ring portion includes a first bar portion on afourth side of the semiconductor die. The first bar portion is insulatedfrom the first ring portion. In another embodiment, the ring portionfurther includes a second bar portion on the fourth side of thesemiconductor die. The first bar portion, the second bar portion and thefirst ring portion are insulated from each other.

In one embodiment, the first surface of the inner portion defines afirst plane. The ring portion is formed co-planar with the first plane.In another embodiment, the inner portion includes an elevated ring thatis formed in a second plane. The second plane is parallel to and spacedapart from the first plane.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIGS. 1-2 are partial top views of an exemplary packaged die accordingto the principles of the present disclosure;

FIG. 3A is an exemplary partial top view of the packaged die of FIG. 1at a later stage of manufacturing;

FIG. 3B is an exemplary top view of a printed circuit board contactpattern corresponding to the packaged die of FIG. 3A;

FIG. 4A is a cross-sectional view of an exemplary implementation of thepackaged die of FIG. 3;

FIGS. 4B-4D are cross-sectional views of additional exemplaryimplementations of packaged dies;

FIGS. 5-10 are partial top views of exemplary packaged dies;

FIG. 11 is a cross-sectional view of an exemplary implementation of thepackaged die of FIG. 10;

FIGS. 12-13 are partial top views of exemplary packaged dies;

FIG. 14 is a cross-sectional view of an exemplary implementation of thepackaged die of FIG. 13, which includes an elevated ring; and

FIGS. 15-22 are partial top views of exemplary packaged dies.

DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the phrase at least one of A,B, and C should be construed to mean a logical (A or B or C), using anon-exclusive logical OR. It should be understood that steps within amethod may be executed in different order without altering theprinciples of the present disclosure.

Referring now to FIG. 1, a partial top view of a package is shown. Thepackage includes a conductive lead frame 100. For example, the frame 100may be made of metal, and may be formed by stamping a sheet of metal.Once the frame 100 is formed, a die 104 is mounted to the frame 100. Thedie 104 may be mounted directly to the frame 100 or to an intermediarylayer (not shown). For example only, the intermediary layer may be aninsulator to prevent shorts between the die 104 and the frame 100.

In various implementations, it may be desirable for a face of the die104 that contacts the frame 100 to be electrically continuous. Forexample only, the face of the die 104 may include ground connections,and the conductive frame 100 can therefore decrease the resistancebetween the ground connections.

The die 104 may also be connected to the frame 100 via bond wires 116,such as bond wires 108 and 112. In addition, bond wires 116 mayelectrically connect the die 104 to bond fingers 120 of the package. Forease of illustration, only some of the bond fingers 120 are shown. Thebond fingers 120 may be present on all four sides of the frame 100, ormay be limited to one or more sides.

Once bond wires are connected, the die 104 is enclosed in a casing(shown in FIG. 4A) that secures the frame 100. The casing may include anencapsulating material, such as epoxy, plastic, or resin, and may beapplied using an injection molding process.

Referring now to FIG. 2, it may be desirable to split the frame 100 intotwo pieces to, for example, create a ground plane 124 and a power ring128. The ground plane 124 can provide ground connections to the die 104via bond wires such as the bond wires 108 and/or through directionconnection to the die 104. The power ring 128 may provide operatingpower to the die 104, such as via the bond wires 112.

In order to electrically separate the power ring 128 from the groundplane 124, connecting sections 132 indicated by circles may be removed.Removal of the connecting sections 132 is performed after the frame 100and the die 104 have been encased. In this way, disconnected sections ofthe frame 100 are fixed in place by the casing. Removal of theconnecting sections 132 may be effected using any of a number ofappropriate milling techniques and/or equipment including, for example,lasers, router bits, saw blades, etc. For example, where higher cuttingprecision is desired (such as, in the case of a localized trench orcut), lasers, router bits or small-diameter saw blades may be used; onthe other hand, where lower cutting precision is sufficient (such as, inthe case where one side of the frame 100 is cut), large-diameter sawblades may be used.

Referring now to FIG. 3A, the power ring 128 is shown separated from theground plane 124. For example, a cavity 140 is present where one of theconnecting sections 132 of the frame 100 was previously located.Removing the connecting sections 132 means that the connecting sections132 no longer conduct electricity between different portions of theframe 100. For example only, the connecting sections 132 may becompletely removed. Alternatively, vestigial pieces of the connectingsections 132 may remain, such as is shown in FIG. 3A. It should befurther noted that while the edges of the cavity 140 shown in FIG. 3Aare straight, such edges may also be round or curved, depending on thetype of technique and/or equipment that is used to perform the removal.

Material from the frame 100 may be removed by any suitable process. Forexample only, mechanical removal, chemical etching, or laser removal maybe performed. Mechanical removal may be performed using, for exampleonly, a router, a saw, a drill, or a high pressure stream of fluid.Chemical etching may include using photolithography to define theportions of the frame 100 that will be removed.

Referring now to FIG. 3B, a contact pattern 150 may be formed on aprinted circuit board to receive the packaged die of FIG. 3A. Thecontact pattern 150 includes lead contact areas 154, ring contact area158, and plane contact area 162. Each of the lead contact areas 154allows an electrical connection with one of the bond fingers 120. Thering contact area 158 allows an electrical connection with the powerring 128, and the plane contact area 162 similarly allows an electricalconnection with the ground plane 124.

The contact pattern 150 may be modified based on the arrangement of thepackaged die that will be mounted to the printed circuit board. Invarious implementations, the contact pattern 150 may accommodatemultiple types of packaged dies. For example only, some packaged diesmay not include a bond finger corresponding to each of the lead contactareas 154. In another example, the ground plane 124 of some packageddies may be smaller than the plane contact area 162.

Solder may provide an electrical and a physical connection between thecontact pattern 150 and the packaged die. Each contact area of thecontact pattern 150 may be connected to a trace on the printed circuitboard. For example only, a multi-layer printed circuit board may includea ground plane. The ground plane may be connected to the plane contactarea 162, such as through an array of vias.

Referring now to FIG. 4A, a cross-sectional side view of the packageddie of FIG. 3A is shown. The die 104 is shown surrounded by a casing200. As described above, the casing 200 may include one or more pieces,or may be a coating applied to the die 104. In FIG. 4A, the bond fingers120 are part of leads 204. The lead 204 may be formed from a continuouspiece of material, such as metal, or may be formed from a joining ofmultiple pieces. The lead 204 may be formed in the shape shown in FIG.4A by bending, which may be performed before or after mounting the die104 to the frame 100.

In the example of FIG. 4A, the lead 204 extends from the edge of thecasing 200. Various other lead structures are possible. Three furtherexamples are given in FIGS. 4B, 4C, and 4D. In FIG. 4B, lead 220 is bentso that the bottom portion of the lead 220 remains within the confinesof the casing 200, as viewed from a top view. This may reduce the amountof space required for the packaged chip on the circuit board.

In FIG. 4C, lead 230 is enclosed by the casing 200. The bond finger 120portion of the lead 230 may be connected to a bottom portion of the lead230 using a through-hole, or via. In FIG. 4D, a lead 240 is located onthe bottom of the casing 200. The bond finger 120 may serve as not onlythe seat of the bond wire, but also as the portion of the lead 240 thatwill contact the circuit board.

Returning now to FIG. 4A, the ground plane 124 and the power ring 128are exposed at the bottom of the casing 200. The ground plane 124 andthe power ring 128 may be flush with the bottom surface of the casing200 or may protrude beyond the bottom surface of the casing 200. Thismay allow for more reliable seating against a circuit board that is notperfectly flat.

Although a true cross-section may show only a single one of the bondwires, for purposes of illustration, bond wire 108, bond wire 112, andbond wire 116 are all shown in FIG. 4A. The cavity 140 between theground plane 124 and the power ring 128 is created to separate the powerring 128 from the ground plane 124. This cavity may be filled withadditional encapsulating material. For example only, the cavity 140 maybe filled with the same compound of which the casing 200 is made.

A further packaging process step may include trimming the leads 204 toreduce their protrusion beyond the edges of the casing 200. In addition,the leads 204 may be plated for corrosion resistance and more reliableelectrical connection. The leads 204 may be flexible to increase thereliability of connections to a circuit board that is less thanperfectly flat.

Although labeled as ground and power for ease of explanation, the groundplane 124 and the power ring 128 may carry other signals between the die104 and the circuit board. For example only, the roles may be reversed,with power being provided to the die 104 via the ground plane 124 and aground connection being provided by the power ring 128.

In another example, negative and positive power supplies, or vice versa,may be provided by the ground plane 124 and the power ring 128,respectively. Ground connections may then be provided by one or more ofthe leads 204. In yet another example, one of the ground plane 124 andthe power ring 128 may provide input power to the die 104, while theother carries output power. For example, such an arrangement may be usedwhen the die 104 is a voltage regulator or converter.

Referring now to FIG. 5, a die 304 is connected to a frame 308. Whenconnecting portions of the frame 308 are removed, the resultingstructure is shown in FIG. 6. The frame 308 is seen to be split into aplane 312, a partial ring 316, and a bar 320. For clarity ofillustration, bond wires connecting the die 304 to the bar 320 are notshown. In addition, additional bond wires may connect the die 304 toadditional portions of the partial ring 316. For example only, bondwires may radiate from the die 304 in all directions.

The plane 312, the partial ring 316, and the bar 320 can be used tocarry any signals to and from the die 304. In one example, the plane 312provides ground connections to the die 304. The partial ring 316provides analog power to the die 304, and the bar 320 provides digitalpower to the die 304. This may reduce the amount of power supply noiseintroduced from the digital componentry of the die 304 into the analogcomponentry of the die 304 and vice versa.

Referring now to FIG. 7, another frame 350 is shown. When connectingsections are removed, a plane 354, a partial ring 358, a bar 362, andtwo sub-bars 366 and 370 are formed. Although shown as separately formedin FIG. 7, sub-bars 366 and 370 may initially be connected together. Theconnecting portion can be removed as part of the packaging process.

For example only, the plane 354 may provide a ground connection to thedie 304. As used in this application, ground means a common potentialthat may or may not be the same as earth ground. The common potentialmay be connected to a system ground of a system in which the die 304 isused. The partial ring 358 may provide analog power to the die 304,while the bar 362 provides digital power to the die 304.

The sub-bars 366 and 370 may provide additional power supplies to thedie 304. For example only, the sub-bars 366 and 370 may provide power atdifferent voltages than that provided by the bar 362 or the partial ring358. For example only, the power supplied by the sub-bars 366 and 370may be for input/output circuitry operating at two different voltagelevels. This may allow the die 304 to interface with components thateach operate at different voltages than the internal circuitry of thedie 304.

Referring now to FIG. 9, a frame 400 is shown. When connecting portionsof the frame 400 are removed, the resulting structure is shown in FIG.10. In FIG. 10, a plane 408 and concentric inner and outer rings 412 and416 are created. The die 304 may connect directly to the plane 408 ormay connect via bonding wires (not shown).

Referring now to FIG. 11, a cross-sectional view of the package of FIG.10 is shown. Gaps 420 and 422 result from separating the inner ring 412from the plane 408 and the outer ring 416.

Referring now to FIG. 12, a frame 500 is shown. The frame 500 appearssimilar to the frame 400 of FIG. 9 in this top view. As shown in FIG.13, only some interconnecting portions are removed from the frame 500.The resulting portions of the frame 500 form a plane/ring 508 and a ring512.

Referring now to FIG. 14, differences between the frame 500 of FIG. 12and the frame 400 of FIG. 9 can be seen. The plane/ring 508 includes anelevated ring, as seen at 520 and 522. Bond wires 530 connect the die504 to the elevated ring portion of the plane/ring 508. Elevating thering may make the wire-bonding faster, cheaper, or less error-prone, andmay result in more reliable wire bonds.

Referring now to FIG. 15, a frame 600 is shown with a die 604. In FIG.16, some interconnecting portions of the frame 600 have been removed tocreate a plane/ring 608, a partial ring 612, and a bar 616. The ringportion of the plane/ring 608 may be elevated, as shown in FIG. 14.

Referring now to FIG. 17, a frame 700 is shown with a die 704. In FIG.18, interconnecting portions of the frame 700 have been removed. Aplane/ring 708 may include an elevated ring, similar to FIG. 16. Apartial ring 712, a bar 716, and sub-bars 720 and 724 are also formedfrom the frame 700.

Frames may be created for which part or all of one or more bars aremissing. For example only, referring now to FIG. 19, a frame 800 isshown with a die 804. In FIG. 20, interconnecting portions of the frame800 have been removed. The die 804 is mounted to a plane 808. A partialring 812 encircles two sides of the plane 808. A bar 816 is formed on athird side of the plane 808.

Together, the partial ring 812 and the bar 816 partially encircle theplane 808, leaving the fourth side of the plane 808 open. By omittingmaterial on the fourth side of the plane 808, the amount of metalrequired for the frame 800 may be reduced, which may decrease the unitcost of the frame 800. One or more additional rings (not shown) maycompletely or partially encircle the plane 808. The additional rings maybe concentric, and may partially encircle different sides of the plane808.

In another example, referring now to FIG. 21, a frame 900 is shown witha die 904. In FIG. 22, interconnecting portions of the frame 900 havebeen removed. The die 904 is mounted to a plane 908. A bar 912 islocated on one side of the plane 908. In this example, the remainingthree sides of the plane 908 are open, with no associated bar or ring.

Although various examples have been shown in the preceding figures,additional partial and/or full rings may be included. In addition, anyring may be split into partial rings, bars, or sub-bars. In addition,part or all of any ring may be formed in the same plane as any otherring, or may be elevated or lowered with respect to any other ring.

In addition, although various examples of uses for connections have beengiven above, additional uses for each section of a frame are possible.In various implementations, a single package may be used with differenttypes of dice. Depending on the particular die, a portion of the framemay perform different functions. For example only, a portion of theframe may be used for analog power if one type of die is attached, whilebeing used for digital power if another type of die is attached. Inaddition, based on the particular die placed in the package, certainconnecting sections may be left in place instead of being removed. Thismay allow a single frame structure to accommodate multipleconfigurations of rings and bars.

The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims.

1. A packaged semiconductor comprising: a conductive integral frame thatincludes an inner portion and a ring portion encircling the innerportion; a semiconductor die that is mounted to a first surface of theinner portion of the conductive frame; and a casing that supports theconductive frame and covers the semiconductor die, wherein sections ofthe conductive frame that connect the inner portion to the ring portionare removed after the casing is applied to the conductive frame.
 2. Thepackaged semiconductor of claim 1, wherein a face of the ring portionand a face of at least part of the inner portion are exposed on anexternal surface of the casing.
 3. The packaged semiconductor of claim2, wherein all of the inner portion that is opposite the first surfaceis exposed on the external surface of the casing.
 4. The packagedsemiconductor of claim 2, wherein the face of the ring portion and theface of at least part of the inner portion are flush with a bottomsurface of the casing.
 5. The packaged semiconductor of claim 2, whereinthe face of the ring portion and the face of at least part of the innerportion protrude beyond a bottom surface of the casing.
 6. The packagedsemiconductor of claim 2, further comprising: a plurality of leads thatare exposed on the external surface of the casing; and a plurality ofbond wires that respectively connect the plurality of leads to thesemiconductor die.
 7. The packaged semiconductor of claim 1, wherein thering portion includes a continuous first ring portion encircling atleast three sides of the inner portion.
 8. The packaged semiconductor ofclaim 7, wherein the continuous first ring portion completely encirclesthe inner portion.
 9. The packaged semiconductor of claim 7, wherein thering portion includes a first bar portion on a fourth side of thesemiconductor die, and wherein the first bar portion is insulated fromthe first ring portion.
 10. The packaged semiconductor of claim 7,wherein the ring portion includes a first bar portion and a second barportion on a fourth side of the semiconductor die, and wherein the firstbar portion, the second bar portion, and the first ring portion areinsulated from each other.
 11. The packaged semiconductor of claim 1,wherein the ring portion includes a plurality of portions insulated fromeach other.
 12. The packaged semiconductor of claim 1, wherein the firstsurface of the inner portion defines a first plane, and wherein the ringportion is formed co-planar with the first plane.
 13. The packagedsemiconductor of claim 1, wherein: the first surface of the innerportion defines a first plane, the ring portion is formed co-planar withthe first plane, and the inner portion includes an elevated ring that isformed in a second plane, wherein the second plane is parallel to andspaced apart from the first plane.
 14. The packaged semiconductor ofclaim 13, further comprising a plurality of bond wires that connect thesemiconductor die to the elevated ring.
 15. The packaged semiconductorof claim 1, further comprising a plurality of bond wires that connectthe semiconductor die to the ring portion.
 16. The packagedsemiconductor of claim 1, further comprising a plurality of bond wiresthat connect the semiconductor die to the inner portion.
 17. Thepackaged semiconductor of claim 16, further comprising an insulatingmaterial between the semiconductor die and the inner portion.
 18. Thepackaged semiconductor of claim 1, wherein the casing includes anencapsulating material.
 19. The packaged semiconductor of claim 1,wherein the semiconductor die is a system-on-chip.
 20. A printed circuitboard comprising the packaged semiconductor of claim 1.